The present invention has particular application to motorized pulleys, in which an electric motor is enclosed in a drum, a rotating cylinder having a cylindrical inner surface. In such pulleys known heretofore, oil contained in the pulley is drained from time to time to remove contamination. In the past, contamination has been of three types; degradation from oxidation, contaminants from external sources, and metallic particles generated internally of the drum. Although the use of synthetic oil has practically eliminated oil oxidation, and sealing the transmission from the external environment practically eliminates external contamination, metallic particles are still generated in the course of the operation of the pulley. Small particles have been carried by the oil when it is drained from the pulley; larger particles were attracted by magnetic drain plugs and came out when the plug is removed during an oil change. Removing the contamination by draining the oil is expensive, due to machine down time, labor, materials, and the proper disposal of oil (i.e. EPA requirements). In internal combustion engines, circulating systems are provided, by which the oil is circulated through a filter to remove contamination. Numerous patents have been directed to providing magnetic assemblies for removing metallic particles that might otherwise bypass the filter. For example, Brunsting U.S. Pat. No. 5,556,540 discusses prior art patents and proposes to improve upon them by inserting within the filter magnetic members, either side by side permanent magnets, or a single sheet of magnetic material. Such assemblies are canisters or cartridges, which are intended to be discarded or reconditioned, and the magnetic member itself is intended to be released from the canister for reuse of the assembly (Column 7, lines 40-44). Providing a pump and circulating system to circulate oil from the pulley through a filter located outside the pulley is not only complicated, likely to lead to damage of the external filter, and expensive but, for the motorized conveyer pulley it is impractical to use this type of system because the pulley drum rotates and the shafts are stationery.
Poilier, U.S. Pat. No. 5,383,534 suggests installing a flexible magnetic member into the drain pan of an internal combustion engine, one end of the flexible member or members being connected to a drain plug so that the flexible members can be pulled from the engine when the plug is withdrawn. Again, the magnetized strip is intended to be withdrawn from time to time, presumably along with the oil in the crankcase.
Kinser, U.S. Pat. No. 5,066,071 discloses a truck wheel bearing hubcap assembly with a "magnetic flag 20" being suspended pivotally from a rod in the center of the hubcap. It is viewable through a transparent window, so that a truck operator can tell when the strip has collected particles, withdraw it, clean it off, and replace it. Oil in the hub is agitated by the motion of the hub itself, but the flag is supposed to remain relatively stationery with respect to the ground, because it is gravity biased, well lubricated and pivotally mounted.
There is a demand for a non-maintenance motorized pulley, in which the oil is not changed for the entire life of the pulley At the same time, as has been indicated, providing a circulating system with an external filter is impractical.
One of the objects of this invention is to provide a magnetic particulate trap that will remove metal particles of any size from the oil in the pulley for the entire anticipated life of the pulley, without changing oil or making any further provision for removal of metallic particles.
Another object is to provide such a device which is inexpensive, readily manufactured, and dependable throughout the anticipated life of the pulley.
Other objects will become apparent to those skilled in the art in the light of the following description and accompanying drawing.